Regional cerebral blood flow pattern in subcortical propagation of focal seizures in newborn monkeys

Establishing a photothrombotic 'ring' stroke model in adult mice with late spontaneous reperfusion: quantitative measurements of cerebral blood flow and cerebral protein synthesis

This study sought to establish the photothrombotic 'ring' stroke model with late spontaneous reperfusion in adult mice. By applying a 3.0-mm diameter laser ring-beam (514 nm, 0.21 mm thick, 0.65 W/cm2) onto the exposed skull for 60 secs with concurrent erythrosin B (4.25 mg/kg) intravenous infusion for 15 secs, the centrally located cortical region within the ring locus was progressively encroached by an annular ring-shaped perfusion deficit. In this region, local cerebral blood flow (lCBF) measured by laser-Doppler flowmetry declined promptly after irradiation to 43% of the baseline value at 30 mins poststroke. Using double tracer autoradiography, quantitative lCBF measured with [14C]iodoantipyrine was 46 to 17 to 58 ml/100 g/mins at 4 h to 48 h to 7 days postischemia in this area. Cerebral protein synthesis (CPS), as detected by [3H]leucine incorporation into protein, transiently decreased to 57% to 38% to 112% at 4 h to 48 h to 7 days postischemia in the center region. Morphologically, some neurons in the center region appeared swollen at 4 h. At 48 h, the majority of neurons were severely swollen with eosinophilia and pyknosis, whereas at 7 days poststroke' the tissue morphology became partly restored. The center within the mouse photothrombotic ring lesion thus exhibits reversible alterations of local CBF, CPS and tissue morphology that are reminiscent of the cortical penumbra in other models of focal cerebral ischemia.

Quantitative measurement of local cerebral blood flow in the anesthetized mouse using intraperitoneal [14C]iodoantipyrine injection and final arterial heart blood sampling

Autoradiographic measurement of local cerebral blood flow (CBF) with [14C]iodoantipyrine (IAP) is limited in mice by the difficulty in cannulating vessels and the blood loss for repeated blood sampling. The authors modified and validated the method to measure local CBF with [14C]IAP in mice by combining intraperitoneal tracer application with a single blood sampling from the heart at the end of the experiment. Experiments were carried out in male SV129 mice under halothane anesthesia. After intraperitoneal administration of 15 microCi [14C]IAP, arterial blood samples were collected repeatedly and anesthetized animals were immersed in liquid nitrogen. In addition, frozen blood from the heart was sampled to obtain the final blood [14C]radioactivity. Correlation analysis between the sampling time and [14C]radioactivity of the arterial blood revealed a highly significant linear relationship (P < 0.001, r = 0.978) and a lag time of the [14C]tracer in arterial blood of 3.3 +/- 0.6 seconds. [14C]radioactivity of the final arterial blood sample (444 +/- 264 nCi/mL) was almost equal to that of the heart blood (454 +/- 242 nCi/mL), and the absolute difference in each animal was 3.3 +/- 4.2% (mean +/- SD). The convolution integrals for the CBF calculation were determined either by integrating the radioactivity of individual arterial blood samples or by assuming a linear rise from [14C]tracer lag time after intraperitoneal [14C]IAP injection to the value measured in the blood sample from the frozen heart. Regional flow values calculated by the two methods differed by less than 11% (not significant). This method allows the quantitative measurement of local CBF in anesthetized mice without any vessel catheterization and will make mutant mice a more powerful tool to elucidate the molecular mechanisms of brain injuries by combining flow studies with molecular-biological methods.

Pathophysiological mechanisms of brain damage from status epilepticus

Human status epilepticus (SE) is consistently associated with cognitive problems, and with widespread neuronal necrosis in hippocampus and other brain regions. In animal models, convulsive SE causes extensive neuronal necrosis. Nonconvulsive SE in adult animals also leads to widespread neuronal necrosis in vulnerable regions, although lesions develop more slowly than they would in the presence of convulsions or anoxia. In very young rats, nonconvulsive normoxic SE spares hippocampal pyramidal cells, but other types of neurons may not show the same resistance, and inhibition of brain growth, DNA and protein synthesis, and of myelin formation and of synaptogenesis may lead to altered brain development. Lesions induced by SE may be epileptogenic by leading to misdirected regeneration. In SE, glutamate, aspartate, and acetylcholine play major roles as excitatory neurotransmitters, and GABA is the dominant inhibitory neurotransmitter. GABA metabolism in substantia nigra (SN) plays a key role in seizure arrest. When seizures stop, a major increase in GABA synthesis is seen in SN postictally. GABA synthesis in SN may fail in SE. Extrasynaptic factors may also play an important role in seizure spread and in maintaining SE. Glial immaturity, increased electronic coupling, and SN immaturity facilitate SE development in the immature brain. Major increases in cerebral blood flow (CBF) protect the brain in early SE, but CBF falls in late SE as blood pressure falters. At the same time, large increases in cerebral metabolic rate for glucose and oxygen continue throughout SE. Adenosine triphosphate (ATP) depletion and lactate accumulation are associated with hypermetabolic neuronal necrosis. Excitotoxic mechanisms mediated by both N-methyl-D-aspartate (NMDA) and non-NMDA glutamate receptors open ionic channels permeable to calcium and play a major role in neuronal injury from SE. Hypoxia, systemic lactic acidosis, CO2 narcosis, hyperkalemia, hypoglycemia, shock, cardiac arrhythmias, pulmonary edema, acute renal tubular necrosis, high output failure, aspiration pneumonia, hyperpyrexia, blood leukocytosis and CSF pleocytosis are common and potentially serious complications of SE. Our improved understanding of the pathophysiology of brain damage in SE should lead to further improvement in treatment and outcome.

Postnatal changes in local cerebral blood flow measured by the quantitative autoradiographic [14C]iodoantipyrine technique in freely moving rats

The postnatal changes in local cerebral blood flow in freely moving rats were measured by means of the quantitative autoradiographic [14C]iodoantipyrine method. The animals were studied at 10, 14, 17, 21 and 35 days and at the adult stage. At 10 days after birth, rates of blood flow were very low and quite homogeneous in most cerebral structures except in a few posterior areas. From these relatively uniform levels, values of local cerebral blood flow rose notably to reach a peak at 17 days in all brain regions studied. Rates of blood flow decreased between 17 and 21 days after birth and then increased from weaning time to reach the known characteristic distribution of the adult rat. The postnatal evolution of local cerebral blood in the rat is in good agreement with previous studies in other species such as dog and humans that also show higher rates of cerebral blood flow and glucose utilization at immature stages. However, in the rat, local cerebral blood flow and local cerebral glucose utilization are not coupled over the whole postnatal period studied, since blood flow rates reach peak values at 17 days whereas glucose utilization remains still quite low at that stage. The high rate of cerebral blood flow in the 17-day-old rat may reflect the energetic and biosynthetic needs of the actively developing brain that are completed by the summation of glucose and ketone body utilization.

Regional cerebral blood flow and kainic acid-induced focal limbic seizures in cats

An experimental limbic seizure was induced in cats by microinjection of kainic acid into the left amygdala. Measurement of regional cerebral blood flow (rCBF) in the limbic structure and cerebral cortex was performed by means of the hydrogen clearance method. Immediately after the development of continuous multiple spikes, rCBF increased about 2-fold in the left amygdala (LA) and remained so during the seizure. When continuous multiple spikes were transmitted to the left hippocampus (LH), rCBF in the LH increased to 140% of the baseline value, but in the right amygdala (RA) and left sensorimotor cortex (LCx) it remained unchanged. During limbic seizure in which spike discharges propagated to the LCx, rCBF in the LA, RA, LCx and LH increased to 220%, 130%, 120% and 190%, respectively. In the interictal stage in which interictal spike discharges intermittently appeared in the LA, rCBF returned to baseline values in the primary and secondary foci. The results show that rCBF increased almost simultaneously with the development of the seizure in the primary focus and the areas where seizure propagation were observed, and returned to baseline value once the seizure had disappeared. During the interictal stage, rCBF in the primary focus was only slightly increased in spite of persistence of interictal spike discharges.

Measurement of local cerebral blood flow with [14C]iodoantipyrine in the mouse

Local cerebral blood flow was measured in the mouse by means of the [14C]iodoantipyrine method. This method has been previously used in the monkey, dog, cat, and rat, but its application to small mammals such as the mouse requires special attention to potential sources of error. The small size of the mouse brain requires special attention to the rapid removal and freezing of the brain to minimize effects of postmortem diffusion of tracer in the tissue. Because of the relatively low diameter/length ratios of the catheters needed for arterial sampling in small animals, substantial errors can occur in the determination of the time course of the [14C]iodoantipyrine concentration in the arterial blood unless corrections for lag time and dead space washout in the catheter are properly applied. Local cerebral blood flow was measured in seven awake mice with appropriate care to minimize these sources of error. The values were found to vary from 48 ml/100 g/min in the corpus callosum to 198 ml/100 g/min in the inferior colliculus. The results demonstrate that the [14C]iodoantipyrine method can be used to measure local cerebral blood flow in the mouse and that the values in that species are, in general, somewhat higher than those in the rat.

[18F]fluorodeoxyglucose positron emission tomography in refractory complex partial seizures

Positron emission tomography with simultaneous electroencephalographic monitoring was performed with [18F]fluorodeoxyglucose in 20 patients with complex partial seizures who had normal computed tomographic scans. Seven patients had only unilateral epileptiform discharges on the electroencephalogram, 3 had predominantly unilateral discharges, and 10 had nonlocalized epileptiform abnormalities. Positron emission tomography showed a hypometabolic lesion in 16 of the 20 patients. Pathological changes in the hypometabolic region were found in postoperative specimens in 4 of 5 patients studied. Positron emission tomography was unaffected by the seizure frequency, state of alertness, or number of spike discharges during the scan. There was a tendency for patients to have higher overall metabolic rates when taking less medication. Seizures occurring during [18F]fluorodeoxyglucose uptake in 3 patients produced a hypermetabolic area at the interictal hypometabolic focus. Positron emission tomography sometimes showed more widespread hypometabolism than suspected on the basis of the scalp-recorded electroencephalogram. The frontal lobe showed a greater degree of hypometabolism than the temporal lobe in 3 patients. Focal lesions may be identified by positron emission tomography even if the electroencephalographic abnormality is not well localized.

Epileptic patterns of local cerebral metabolism and perfusion in humans determined by emission computed tomography of 18FDG and 13NH3

Seventeen patients with partial epilepsy had electroencephalographic (EEG) monitoring concurrent with cerebral positron emission computed tomography (PECT) after 18F-fluorodeoxyglucose (18FDG) and 13N-ammonia (13NH3) were given intravenously as indicators of local cerebral glucose utilization (LCMRglc) and relative perfusion, respectively. In 12 of 15 patients who had unilateral or focal electrical abnormalities, interictal 18FDG scan patterns clearly showed localized regions of decreased (14 to 58%) LCMRglc that correlated anatomically with the eventual EEG localization. These hypometabolic zones appeared normal on x-ray computed tomography in all but 3 patients and were unchanged on 18FDG scans repeated on different days. In 5 of 6 patients who underwent anterior temporal lobectomy the interictal 18FDG scan correctly detected the pathologically confirmed lesion as a hypometabolic zone, and removal of the lesion site resulted in marked clinical improvement. In contrast, the ictal 18FDG scan patterns clearly showed foci of increased (82 to 130%) LCMRglc that correlated temporally and anatomically with ictal EEG spike foci and were within the zones of interictal hypometabolism (three studies in 2 patients). 13NH3 distributions paralleled 18FDG increases and decreases in abnormal zones, but 13NH3 differences were of lesser magnitude. When the relationship of 13NH3 uptake to local blood flow found in dog brain was applied as a correction to the patients' 13NH3 scan data, local alterations in perfusion and glucose utilization were usually matched in both the interictal and the ictal state. We conclude that the interictal 18FDG-PECT scan is useful in aiding localization of the dysfunctional cerebral zone most likely to be responsible for seizures in patients being considered for anterior temporal lobectomy. With further development, emission computed tomography may help in better categorizing the various forms of the disorder and in elucidating the basic mechanisms of epilepsy in humans.

Propagation of focal motor seizures in the pubescent monkey

The rate of local cerebral glucose utilization was determined for quantification of energy metabolism in macrostructures of the sensorimotor system during propagation of focal motor seizures in 24-month-old monkeys. The rate was measured in 4 control animals and in 4 monkeys each with seizures limited to the contralateral face, seizures of the contralateral face and upper extremity, and bilateral expression of seizures. Glucose utilization increased significantly, primarily unilaterally, with propagation. The increase was greatest in the sensory and motor cerebral cortices, putamen, and globus pallidus, was somewhat less in sensory and motor thalamic relay nuclei, and was least in the cerebellar cortex.

Local cerebral glucose utilization in newborn and pubescent monkeys during focal motor seizures

The [14C]deoxyglucose method was used to determine the rate of local cerebral glucose utilization (LCGU) in newborn and pubescent monkeys during focal motor seizures induced by injecting penicillin into the face-hand area of the right motor cortex. Seizures were studied in 3 newborn and 6 pubescent monkeys, and 3 newborn and 4 pubescent monkeys were used as controls. In controls, the pattern of glucose utilization within structures of the sensorimotor system was quite differenet at the two age levels; newborns showed far less activity, especially in the neocortex and striatum. In the monkeys with seizures, the unilateral increase in LCGU relative to the controls was greater in newborn than in pubescent monkeys except in the cerebral and cerebellar cortices. The increased glucose utilization in cortical and subcortical structures of the newborns was ipsilateral to the discharging lesin and lacked the well-defined pattern seen in the pubescent monkeys. In general, newborn brain was capable of supporting a focal motor seizure but lacked the precise clinical and electrographic expressions or efficient energy metabolism that accompany maturation of the brain at puberty.

Effects of manipulation of the sensorimotor system on focal motor seizures in the monkey

During focal motor seizures induced by injecting penicillin into the face-hand area of the right motor cortex of 24-month-old monkeys, the sensorimotor system was manipulated by three methods. Elimination, by a paralytic agent, of proprioceptive input from contracting muscles and joints did not alter the electrographic expression of the seizure or the pattern of local glucose utilization in cortical or subcortical components of the sensorimotor system. An overall increase in the rate of energy metabolism occurred in the paralyzed monkeys with electrographic seizures. Cryogenic destruction of up to 90% of the ipsilateral ventral caudal globus pallidus had no effect on electrographic or clinical expression of the seizure. Electrical stimulation of the ipsilateral ventral caudal globus pallidus caused reproducible maximum expression of electrographic and clinical seizure phenomena for the 90-second duration of the stimulus.